Assyrian and Babylonian Exiles

I found this interesting.  Never really noticed it before.  It gives an explanation of why there was both an Assyrian exile and then many years later a Babylonian exile. 

Why the two?  Why didn't God take care of the problem all at once?  

Ezekiel 22:30-31(NKJV)

So I sought for a man among them who would make a wall, and stand in the gap before Me on behalf of the land, that I should not destroy it; but I found no one. 

Therefore I have poured out My indignation on them; I have consumed them with the fire of My wrath; and I have recompensed their deeds on their own heads,” says the Lord GOD.

Looks to me like God was giving them a second chance.  God dished out the first punishment to the Northern Kingdom of Israel hoping that Judah would take notice.  But God found no one willing to stand in the gap so God brought the hammer down again!